Add durable cross-device agent messaging

[cyzus]

Summary

• reuse the existing Devices control-grant and Suzent HTTP channel as the cross-backend Agent transport
• expose paired backends through agent_list as stable peer:<peer_id> addresses
• route agent_send through the existing durable message table with a suzent_peer transport, preserving the same lease, retry, idempotency, and terminal-state machinery as local delivery
• add a small PeerAgentTransport adapter shared by send, read, stop, and the inbox dispatcher
• add POST /channels/suzent/inbox, which acknowledges only after the receiver commits the message to its local durable inbox
• add peer-scoped session read and stop endpoints for agent_read and agent_stop
• bind every authenticated caller to its own suzent:<device_id> namespace so a peer cannot select, inspect, or stop arbitrary local chats
• keep remote delivery retryable for offline devices with bounded exponential backoff and receiver-side idempotent ACKs
• preserve remote Agent IDs across LAN/Tailscale address changes by carrying the existing installation node_identity into the peer store
• share transcript bounding and the process-wide peer store instead of duplicating queue, HTTP-auth, or transcript logic

Why

PR #101 added the local durable Agent inbox. Suzent already had device discovery, pairing, scoped peer tokens, reachability, and an agent-to-agent channel, so a separate relay stack would duplicate those responsibilities. This PR bridges the existing Nodes transport to the durable inbox and keeps all retry/state transitions in one queue implementation.

Security

• all new remote routes require the existing agent-scope device grant
• identity comes from the verified bearer token, never from a request body
• inbox/read/stop always target the authenticated peer's dedicated session
• optional legacy streaming session names are normalized below the authenticated peer namespace
• message IDs and content are bounded and receiver ACKs are validated before marking outbound delivery complete

Verification

• uv run --no-sync pytest -m "not sandbox" -q — 983 passed
• focused database, inbox, Nodes, routing, auth, and Agent tool tests — 100 passed
• final focused regression after HTTP adapter hardening — 86 passed
• npm test — 80 passed
• npm run build — passed
• uv run --no-sync pre-commit run --all-files — passed

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[chatgpt-codex-connector]

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